This invention relates to a rotary feeder valve and more particularly, a rotary feeder valve especially adapted for transferring particulate material such as wood chips from a source to a pressure vessel such as a digester.
In a rotary feeder which transfers particulate material from one environment to another, the shaft supporting the rotor proper may be subject to severe bending stresses. If one environment is at a higher pressure than the other, the force resulting from the imbalance in pressure acting against the area of the rotor is constantly exerted on the rotor as it turns to convey the material in each pocket from the inlet position to the outlet position. This force acting against the rotor tends to bend the rotor shaft from the area of higher pressure.
In a very large rotary feeder used in pulp mills, the force resulting from the imbalance in pressures can reach 175,000 pounds.
Since the position of the higher pressure, and therefore the resulting force, is constant in relation to the rotary feeder, and the rotor and shaft are turning, the force tending to bend the shaft is producing constantly reversing stresses in the shaft. As the rotor and shaft turn 360.degree., a particular portion of the shaft is subjected to a tensile stress, then compressive stress, then tensile stress, etc. Such a condition can result in premature fatigue failure of the shaft.
Fatigue failure normally starts as a microscopic crack, which propagates across the area of the shaft. The crack is initiated by a local condition which causes the local reversing stresses to exceed the capabilities of the material of which the shaft is made. Such a local condition, often called a "notch", can be a metallurgical defect in the material, a metallurgical condition arising from manufacturing processes such as welding, or a sharp corner machined into the shaft. Good design practice for rotating shafts subject to bending calls for the best possible material plus the use of polished surfaces and large radii to avoid creating such a notch.
However, in the construction of rotary feeder, it is not uncommon to assemble the rotor to the shaft by welding or other means which unavoidably have the effect of producing a "notch". Such a condition may cause a shaft to fail by fatigue. The instant invention provides the assembly of a rotor and shaft which minimizes the possibility of fatigue failure by substantial elimination of "notch" conditions. To this end, I provide in a rotor assembly, a rotor body which is equipped with peripherially facing pockets and an axial bore. Interference fitted within the bore is a shaft and the rotor and shaft are equipped with aligned openings in which a pin is mounted.